Automatic backwash traveling bridge rapid sand filters are commonly used for the treatment of municipal and industrial water supplies as well as wastewater effluents. Owners attest to the outstanding performance and economics of the automatic backwash filter. In large part, the automatic backwash filter has stayed in the forefront of treatment technology.
The conventional automatic backwash filter underdrain design has been in use since the late 1940's. The original design was constructed out of steel, which was changed to fiberglass in the mid 1970's. An illustration of the conventional automatic backwash filter design is shown in FIGS. 1(a)-(b). Conventional filter underdrain 100 consists of a series of lateral partitions 101, which divide the filter bed into a multitude of compartments 102. Each compartment is arranged for connection to a separate effluent or backwash port 103. Within each partition 101, above the ports, there is a porous plate 104.
Porous plate 104 acts as a supporting deck or ledge for filter sand media 105 in each separate compartment 102. Porous plates 104 are typically formed from a heavy plastic, such as polyethylene, or ceramics, and are designed to support the weight of the filters and media, which is typically at a depth of 11 inches. In a typical configuration, five porous plates, each measuring 30 inches long by 12 inches wide are installed in each of a sixteen-foot wide compartment, or cell.
The joints between each of these porous plates must be properly sealed to prevent the sand media from leaking into the effluent port area. The porous plate is typically sealed in each cell utilizing caulking. As shown in FIG. 1(b), each porous plate 104 is typically mounted to the partition and secured in place by angle 106 and mounting bolt hardware 107. The space between porous plate 104 and partition 101 is filled with caulking 108.
However, it has been found that this conventional design has certain problems. These include the fact that the field installation of the system is labor intensive, caulking must be installed under clean and dry conditions, the caulking must be applied very consistently to provide an adequate seal, the sand media develops leaks in the caulk area, and the sand media leaks are difficult and expensive to repair.
Accordingly, a system is needed that is substantially leak proof and significantly reduces material and labor installation costs.